What to use as a platform to install FWC over fifth wheel hitch rails?

[hpcbmw]

Next set of questions on my new to me 1980's Keystone. I bought my 2000 F250 shortbed to haul a fifth wheel. The fifth wheel is parked at a lake most of the summer, so I only move it a couple times per year. The FWC is for quick camping trips, etc. Anyway, the fifth wheel hitch I have is removable, all that's left are two rails that sit over the rear axle, from fender to fender. The rails are about 1 1/2" high (a little higher then a standard 2x4) and about 3/4 the width of the bed.

Right now, I've got 3 2x6's under the fwc, just to get it home. I plan on doing a permanent install in the next week or so.

I'm looking at a very firm sheet of 2"x 4'x8' foam at homedepot called thermasheath, here's a link: http://www.homedepot.com/Building-Materials-Insulation-Sheathings/h_d1/N-5yc1vZbaxx/R-100573703/h_d2/ProductDisplay?langId=-1&storeId=10051&catalogId=10053

I'm thinking of slotting this for the two fifth wheel rails, and maybe adding a slot for a 2x4 across the tailgate to even out the pressure, then putting a thin sheet of 4x8 plywood over the top, again to even out the pressure. Then load the FWC. I would use a thinner sheet of sheathing, since I'm using a layer of plywood, but the thinner stuff isn't made from the same very firm material as the 2" sheathing.

Any ideas, input or experience would be appreciated.

 

[Mark W. Ingalls]

Have a look at the bottom of the camper. Mine's not continuously flat. Perhaps you're rails will fall into the gaps?

I did 3/4" foam with strips of 'one-bye' so my sweetie's feet would be warm on winter mornings. You could rip-and-rotate some 'two-bye' and do the same trick, only differnt...

 

[DanoT]

I have the same kind of 5th wheel hitch rails in my truck. I got my custom Phoenix camper built with a 1-1/2" perimeter wood frame with cross pieces on either side of the hitch rails. I then filled the spaces in between the framing and rails with 1-1/2" rigid Polystyrene insulation glued to the bottom of the camper.