Here are a few quidelines:
1) The rear cradles should be at or just foward of the rear crossbar ...
2) The front cradles should be 1' ===> 1 1/2' in front of the front crossbar ... to support the bows of the H18 ....
3) The bows of the boat need to be approximently 6" + 1/2 the width of the towing vehicle back on the trailer from the tip of the trailor tongue ... helps to prevent dents in the side of the trailering vehicle from tight turns .... (learned from experience ....)
4) Rachet straps (4) or one/corner work best, these will be pulling forward ... then you will also need to rig two lines coming forward from the middle of the trailer that you can tie around the frontcrossbar that pull rearward ... this system will hold the boat securely on the trailer ....
5) Use "non" moisture retaining materials to pad your cradles such as styrene and nylon carpet ... moisture in long contact w/ gell coat can cause "gell coat blisters" ..... very time consuming to fix!!!!!
6) Galvanized rims w/ 12" tires work well ...
7) Mudflaps are very helpfull in keeping "road debris" and wheel bearing grease from being thrown up on the hulls .....
If the trailer needs new lights ... it is easiest to just install a new wiring harness w/ the new "LED" sealed lights (last a longgggg time) and solder all connections ... (I have installed double lights on the back ... I was involved in accident one time by being hit from the rear ..... never again as it wasn't a experience I want to repeat ... Please check out the thread here on the H18 Forum .... "H18- The Big Project" ... he did the best job of rebuilding a trailer and a H18 that I've seen ... well explained and documented!!!!!!
There are several threads also here on how to make cheap cradles using PVC pipe material and how to mold them .... (pay close attention to the advice concerning girlfriends/wives and the use of "their" kitchen equipment !!!! ... again hard-learned from experience!!!!)