box to frame connection

[girvin]

Ok I am about to start building my pooor mans bruder exp4. My box is 6'2"x13' I am going to do fiberglassed plywood with 1x2 framing and foam and another layer of ply epoxied in no fasteners ( unless someone has a reason I should do a 1x1 metal frame). Floor is 1/2 ply with no foam. What is the best way to attach the box to my frame? I dont want to introduce moisture into the frame or the wood. I am welding my trailer I was thinking either building little webbings in between runners to bolt through or just using U hanger bolts around the 2x2 cross members the main rails are 2x3.

[KTM_Guy]

I just welded 1.5 X1/8” angle tabs to the frame and used carriage bolts to bolt the cabin to the frame. I probably have 12-16 bolts which would be overkill on a road only trailer but there is a lot of twist and flex on an off-road trailer that I wanted to be on the safe side.

Todd

[girvin]

Yeah that is kind of where I am going did you put epoxy in the holes to keep the water out?

[working on it]

* I used an existing trailer and welded extra tubing onto it to extend to 8 feet. After extending work was done, the perimeter was all rectangular tubing, and two of the three interior crossmembers were C-channel (originals), while the new ones were tubing. All were at the same height, so when I added the 1/2" birch plywood 4x8 to the frame, I made a thick bead of PL adhesive along all points of contact (meaning: everywhere!), and used eight 3/8" carriage bolts thru the C-channel crossmembers to attach. PL adhesive filled the drilled holes for waterproofing.

* Then, I used TB2 adhesive to glue a 1/4" Luan 4x8 atop the birch plywood base and let it dry for a week (with weights holding it flat), and afterwards used several coats of fast-dry polyurethane (the type used for flooring) on the Luan. When it was dry, I used thirty-eight Tek screws going thru both floor sheets into the frame perimeter (again using PL adhesive in each hole). Then, I sealed it all with yet another coat of poly. Though I didn't pre-treat the base birch ply with a poly "mix" to waterproof it, the upper TB2/Luan/polyurethane sealed it from moisture quite well (I had standing water inside my trailer once, with no after effects). The underside of the trailer has been extensively undercoated with rattle-can automotive non-asphaltic spray.

*

carriage and teks.png (256.82 KiB) Viewed 5235 times

[girvin]

wow lol I guess its not going anywhere lol. I was thinking just 8 U hangers and gluing it to the frame Maybe I need more fasteners along the edges.

[swoody126]

a method used in the boating world for thru hull fittings is to slightly over bore a hole in the intended location and fill it w/ thickened pox

once cured center bore thru the pox for your fastener

this prevents moisture from contacting the inner edge grain(inner sides of the hole) of the plywood which is where rot quite/most often begins it's destructive journey

if you are overly concerned about this process you can use FENDER WASHERS extending out over the undisturbed plywood

between the plywood and the metal frame use some of that solid(not foam) squishy rubber tape/weather seal (foam tape can/will hold moisture)

sw

[KTM_Guy]

Yeah that is kind of where I am going did you put epoxy in the holes to keep the water out?

I didn’t mostly because I live in the desert and we don’t see much rain and when we do with the low humidity things dry quickly. If I lived back In the north Midwest or somewhere wet I would have.

Todd

[girvin]

Thanks for all the info! I found a cheap galv place near me so will do the trailer in galv then epoxy the through holes. I did many fasteners that way adding railings to my old sailboat.....Its really tedious lol