I've been doing a ton of looking around regarding trailer builds and yours is top notch! Could you please elaborate on the dimensions of the trailer itself? I'm also looking to build my trailer and in the design stages now. I'm not an engineer by any stretch of the imagination and would like to get some of the more crucial aspects correct...where do the axles go, how long should the tongue be, etc. Also, any tips or advice would be much appreciated. Thanks! And again, excellent work!
Well I'm no expert either but I'll give you some input from my perspective. As for axle placement, I recommend to plan your final setup as much as possible prior to building. For example, I just recently added my rear tire carrier which changed the balance of the trailer with the addition of the weight on the back of the trailer. It wasn't a huge deal for me because that weight was countered by the fuel/water cans at the front of the trailer. But the weight distribution will affect the ideal location for the axle. My axle is positioned about 10" behind the centerline of the trailer to provide a forward bias and some tongue weight to prevent wandering.
As for tongue length, you'll get a wide range of opinions. Personally, I find it not worth the effort to use an adjustable tongue. Some suggest that because they can use a longer tongue length for easier towing and backing on the road, and a shorter length for trails and tighter manuevering. It's a fact that a shorter tongue makes a trailer bit more difficult to back up. But to me its just too much hassle to worry about changing tongue lengths for different conditions. Since my trailer sees use on trails I set it up for optimal behavior on trails and accepted any shortcomings that came with it. I made it as short as possible, but still long enough that the trailer would not contact the truck if the trailer was jacknifed. That length can differ based on trailer shape and tow rig dimensions so build yours accordingly.
The dimension of my trailer are approx. 4x6' for the box. The frame has an outer dimension of 4x6' so the box interior dimensions are slightly shorter than that. The tongue is ~4', and the tire carrier out the back adds another 16" or so. That puts the total length just beyond 11' when you account for the length of the hitch and coupler. I don't have a total width measurement since it's changed a few times with different tires. But the track with was originally set to match the tow rig. IIRC the axle width was 65" from WMS to WMS.