Flatbed build, clearance between truck and camper? Alaskan and 2018 Silverado

SD Shawn

New member
The pickup is a 2018 Silverado 3500 8' pickup bed, duramax. Camper is a 2001 10' CO Alaskan. I removed the pickup bed and will be installing a flatbed.

I am mocking up my camper so I can get going on my flatbed build. The wood is only for mockup purposes, the flatbed is not going to be made out of wood.

This is as tight as I can get it, now I need to figure out how much I need to back it off.

This camper is sitting on a frame made of two 2x4's stacked, so as this sits it is 3" above the truck frame. I have about 1" between the camper and the back of the cab, 1" clearance to open the rear cab doors, and the closest point between the cab roof and the camper is 1/2".

What do you all think those clearances should be? For reference, the top rail on the factory bed sits 1" from the cab.

I am thinking of trying to stick to the 1" between the camper and the cab. Add another 1/2" between the frame and the camper to give me an 1" on the closet point between the camper and the cab.

If I go that route I would build a flatbed that would have my camper sitting 3 1/2" above the truck frame. I plan to add 1" sides to my flatbed that match the footprint of the camper, so the camper will "sit" in the flatbed and shouldn't slide around. Of course I will also mount the camper to the flatbed. I mention the sides so you know that the camper shouldn't slide around, and hit the truck cab.
 

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SD Shawn

New member
There is no one-size-fits-all, but what you have is well too tight.

What I suggest is that you load the camper with at least 4" of clearance between top of cab and underside of cabover, and flex the truck out to see what's what.
Until then you will not know how tight of tolerances you can get away with.
I was thinking something similar. Add another 2x4, and then climb a couple rocks and terraim in the yard and flex things a bit to see how it moves.
 

mog

Kodiak Buckaroo
Not apples to apples as this is for my GZL in the factory bed, but I went with 3 inches of cabover to cab clearance.
1. Aesthetically it looks good to me, while still having a reasonable amount of clearance.
2. Mounted at that height, it also gives me enough clearance to still use the 'Rambox'(s), with the camper on.
3. It gives me 6 inches of clearance under the camper to the bed of the truck, which is a great large storage area for my traction pads, and other recovery gear (shovels, winch anchors, etc)

Sample
PW-3inch.png

That being said, when Earth Cruiser mount the first one of their GZL400s (on a Ram like mine), you can see that it is mounted very close, The customer used it that way, so I guess 'super close' also works. YMMV

EarthcruiserMount1.png
EarthcruiserMount2.png
 
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rruff

Explorer
What I suggest is that you load the camper with at least 4" of clearance between top of cab and underside of cabover, and flex the truck out to see what's what.
I have 2" of gap and that is more than I need... even with my too-flexy frame.

I don't think the torsional flex will change much, and at any rate he has a torsionally stiff frame. Worst case will be driving through a ditch too fast or something similar... I think.
 

mog

Kodiak Buckaroo
As a reminder, you should not see any movement between the cab and the camper on the pitch and yaw axis, it will all be in the roll axis. So the wider your cabover section is, the more movement on the outboard ends, while the center will stay relatively stationary.

axis.jpg

update- YMMV
 
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rruff

Explorer
As a reminder, you should not see any movement between the cab and the camper on the pitch and yaw axis,
Why do you say that? I think his frame should be pretty stiff in torsion, while mine is not... but I get flex on every axis. Definitely some pitch that closes the gap when hitting a sharp bump with the front tires. My camper is also on poly mounts that have a little travel, but the truck frame and camper will flex too.
 
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mog

Kodiak Buckaroo
Why do you say that? I think his frame should be pretty stiff in torsion, while mine is not... but I get flex on every axis. Definitely some pitch that closes the gap when hitting a sharp bump with the front tires. My camper is also on poly mounts that have a little travel, but the truck frame and camper will flex too.
I should have add YMMV to that post as I did to my first post. I can only use my trucks (Ram PW, C4500, MB1017) as reference points, and not all trucks.
And 'wow' your truck flexing in the yaw axis, must really effect handling also :oops:
 

rruff

Explorer
And 'wow' your truck flexing in the yaw axis, must really effect handling also :oops:
🤣I don't think there is ever much of a yaw force...

It handles great... better than I expected with the camper and load.
 

ramblinChet

Well-known member
The only correct source to answer the question you have is your OEM manufacture. When I was building my rig I referenced a document produced by the Ram commercial upfitter team. Off the top of my head I believe the minimum gap was 3-4" or so.

Here is a post received today by good friends currently exploring Canada - it is appropriate for this discussion:

image000000(134).jpg
 

DirtWhiskey

Western Dirt Rat
Sometimes it's nice to have some real space behind the cab on a flatbed setup. Good place to add water tanks, recover gear, step ladder that type of thing, especially with a rear entry like yours where it's hard to put anything behind the camper. I would give 3-4" on the cab over and at least 2" behind the cab. I'll measure the headache rack on my flatbed for reference.
 

rruff

Explorer
The best gap is the least you need. Mine is 2" on a frame that flexes a good amount vertically, and has poly isolators holding the camper, and I can't make it touch.

This rig is currently for sale on ExPo... what do you think that gap is? It's a lot less than mine... fraction of an inch I'd guess.

img_4988-jpeg.818047
 

IdaSHO

IDACAMPER
Ive fitted our flatbed very close. The cross-body box has less than an inch of clearance from the back of the cab.
This cab however, tips forward at the belt line so the window is more like 1-3/4" to 2" from the box.

The cabover, by design, is tight at the rack around 1-1/2"
But completely open where the cabover of the camper sits, placing the underbelly of the cabover about 3" from the top of the cab.
Again, by design.... being a full-timing 4-season setup that seems plenty of snow/ice, I wanted enough room to clear debris that gets in there out by hand.
Also nice to hand enough room to be able to clean in there. So many trucks have them fitted so tight you cannot.

53032453730_68beb65953_b.jpg


53661753540_8b257ae075_b.jpg
 

AbleGuy

Officious Intermeddler
On our last big OH camper/pickup truck combo, we had about 3 1/2” of a gap between truck roof and the bottom of the camper overhead bunk.

To aid in mpgs and aerodynamics, I bought and cut to length a flexible piece of ribber commercial floor cove moulding/trim and glued it along the bottom front edge of the OH camper bunk, to seal off road wind pushing into the dead space under the upper bunk. That actually looked ok and seemed to work well, just FYI

Basically, something like this:
IMG_4908.jpeg

I used the flared out edge to overlap onto the roof of the truck cab, installing this long trim piece at a slight diagonal so it was leaning towards the front of the truck and back towrds the lip of the OH bunk floor.

IMG_4909.jpeg
 
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