Without over thinking this your friend might consider a free standing box that mimics the front profile of the 4 x 7 Little Guy which has a reactively flat front wall below the radius; perhaps a box 1/2 to 2/3 as tall and slightly narrower supported by an L shaped platform resting on and attached to the tongue.
The dual pivoting mechanism could be as simple as a pair of butt hinges on either side with removable pins. I would not think any more bracing would be required than perhaps a sliding rod on the tongue under the box just too keep it from swinging back closed. I've hung 300# doors with a pair of 4x2 inch butt hinges and 3/4 inch screws.
I don't know what all he might be planning to include in the galley but mine, which is a 3 cubic foot box framed with 1 x pine and skinned with 5 mm plywood, weighs less than 10 # empty and when loaded with a butane stove, cookware, utensils, condiments, paper/plastic plates, bowls and drinking cups, and a few cans and boxes of food barely doubles.
Tripling or quadrupling that size say to 42 inches wide, 30 inches tall and 16 inches deep would still be under 100# without a cooler full of ice and beer and if weight distribution is a concern stick the cooler in the back of the cabin. The Little Guys with the extended tongue and cargo platform don't change the location of the axle from the standard model.
Assuming his tow vehicle is capable of towing as little as 1000# I would not see 150-200# of tongue weight a problem.
Waterproofing should not be that big a concern either. If the lid was the radius and the front of the box dropped down to form a table the lid could overlap the lower and the outer edges of both could have a flange that overlapped the sides of the box like roof trim. The rubber/plastic hinges would suffice or just a standard piano hinge covered with a strip of rubber, a la BobHenry. The lids could be opened for quick access without pivoting the whole box outward.
Small portable chuck boxes are fine if you have to carry all your gear in the back of a truck, van or station wagon but my idea of hassle free camping is not having to lift anything other than the lid. A slide out to either side would be workable also - I built one for the storage bay of a 58 VW pickup when I was about 14. A sheet of plywood with 1x6 sides to keep everything on it and a folding wood and canvas stool to hold the open end.
Just my 2-1/2 cents worth.
M C
by Vedette » Fri Jul 24, 2015 1:30 pm 
