Hey Scott....
Welcome to the sand box.
You didn't say in the description of what you plan to build on how many you plan on sleeping in it. Speaking from experience, the HD 40x48 is a good platform for a one-sleeper. My "itty-bitty" doesn't collapse to 4 foot for traveling; but it's only 7'2" to the extremes of the curves. The floor size is 75" x 39", the size of a twin mattress. I did have to put a longer tongue on it. I replaced the stock tongue with a 2 1/2" square tube 28" longer than stock. I probably would have changed the tongue even if I hadn't lengthened it. The stock HD tongue on that trailer left me wondering about it's strength and durability over time. If I hadn't switched the axle to the top of the springs and lowered the frame by 3", I might also have considered building out over the wheels. I probably could have gotten around 54" wide; but it would have still left small wheel well humps inside. The extra ~18" width in the galley would have been nice though.
Any ways, two weekends ago I did an 850 mile round trip in it and fully loaded I don't think it tipped the scales at much over 400 pounds. I lost .1 mpg towing it. True... the two states I traveled through were pretty un-hilly. I think the mountains in Louisiana are the parking lot speed bumps.
Sorry for the long post. I look forward to see some design sketches and the actual build while I do some finishing touches on "itty-bitty' and get started on #2.
