Q: How to attach floor to tube frame? (Magneta 6x8)

[DougGirling]

The warm weather has brought me out of hibernation (unheated garage)and I'm resuming work on the TD. The floor will be the first order of business, which brings me to today's questions:

Q: How best to attach the floor to a tube steel frame?
Q: Do I need to take any measures (e.g., a gasket or a dollop of construction adhesive or caulk at each screw/bolt) to prevent water intrusion through the screw/bolt holes into the tubing or the floor?"

Background/Details:
The frame is a Magneta 6x8 bolt-together utility trailer kit. What makes it slightly unusual is that it designed to take a recessed deck, made with a 4x8 and a 2x8 sheet of ply, that fits flush with the frame. The frame is 2" square tubing and is made 4" oversize to form a 6x8 well to receive the deck. The 3 inner crosspieces are smaller dimension tubing dropped 3/4" to provide the clearance, and the insides of the ends have strips of angle welded 3/4" down to support the ends of the deck.

The floor will sit on top of the frame, rather than drop in like the deck. It will be constructed as in the Generic Benroy (plywood top over a 1x2 frame, with foam insulation and asphault sealant). To accomodate the recessed well, I plan on making the inner cross pieces deeper so that they reach down to the tubing crosspieces.

Bolting it to a channel frame would be straightforward, but a thru-bolt on a tube frame would risk crushing the tube. The shop manuals I have are silent on the matter. Would self-tapping or deck screws be the answer? What advice to you have, Master Yoda?

[madjack]

...definitely seal any and all holes against water intrusion...I use a 1/4" self tapping screw...they are shown as the "standard screw", in the first listing in the following pdf... http://www.redneck-trailer.com/2006/K/K12-K13.pdf
madjack

[DougGirling]

Thanks kindly. Do you have any recommendations for sealant at the hole site?

[madjack]

...I prefer urethane based sealants(and adhesives)...however, in many cases, I have had good luck with siliconized acrylics(cheap painters caulk)...let me clarify as well about the screw I linked to...the maximum length they come in is 2.5"s...I use a single sheet of ply for my floors with an Aluminum angle as a cleat to attach the wall to the floor...a composite type floor would havvta be no more than 2"s thick (or less) for these screws to work...if you do use them, drill a 7/32nd hole and you will be good to go.....
madjack

[looped]

...I prefer urethane based sealants(and adhesives)...however, in many cases, I have had good luck with siliconized acrylics(cheap painters caulk)...let me clarify as well about the screw I linked to...the maximum length they come in is 2.5"s...I use a single sheet of ply for my floors with an Aluminum angle as a cleat to attach the wall to the floor...a composite type floor would havvta be no more than 2"s thick (or less) for these screws to work...if you do use them, drill a 7/32nd hole and you will be good to go.....
madjack

In a few of the build pages i have seen they make sure to mention ways to tighten up the bolts down the road.. with these would that be an issue too? Would the use of loctite red be a good idea for this application?

[McTeardrops]

I do the best I can to make my frames watertight, so the idea of drilling holes in them just goes against the grain. Using the KISS pinciple, I add angle iron clips to the frame and bolt to them, double nutting with nylock nut. Elevator bolts, or button head cap screws have a wide contact area against the wood, and used with a big fender washer, avoid pull- through, and don't tend to put holes in your mattress. I have found some self-tapping screws to be brittle, and prone to breaking. Removing the stub end of one locktited to the frame would be a major pain!