I do a fair bit of dirt track towing on corrugated roads and over the years the most common things to fail and fall off are the guards and winch posts.......conveyer rubber as guards doesn't look pretty but it certainly is practical....I've found that most things bolted on will generally be the first things that fall off.
I have modified a few trailers and have built a few trailers over the years keel rollers can be a real pain in the ass if you stick with the spigot style adjustable I run 75 x 50 4mm uea rails with as many rollers as I can fit through the center of the trailer hard bolted with U bolts to the trailer crossmembers and custom make my own winch posts with 75x75 4mm shs fully welded non height adjustable......
The trailer I have under my 435 tinny is a Redco sportsman that I have put a 1.5t 45mm solid axle and 1250kg slipper springs into........(slippers are ok on dirt roads but not for real 4wding).......i'm in the process of strengthing up the trailer frame by building another frame which will be welded on top of the existing outer frame with a 50mm separation so essentially 2 trailers stacked on top of one another........I built one about 5 years ago for a mate and his 6mtr custom plate boat which he takes bush and carry's a Yamaha Rhino inside the boat......so far no issues.
When I get my ass into gear and do my trailer i'm going to look into making a different carriage frame for mine set up with eye to eye springs bigger guards running 5x150 pcd hubs that will take my 200 series 33'' wheels and tyres for more serious bush trips and for everyday use just keep the 14'' Falcon wheels on...........
Also with the trailer skids what I have done in the past and got the idea off of the pro crabbers up here is to put Blue Stripe poly 50mm on the skids.....put some some alloy flat bar through the polly drill holes through that and your existing trailer skid and bolt the lot together with pan head/coach bolts this takes all of that hull/trailer noise away while towing on corrugated roads and give some cushioning effect also........it works well and is tuff as nails.
Dan