Rebuilding car trailer and welding/bolting galvanized frame

I would not weld to a galvanised chassis,welding and zinc do not mix,when grinding the zinc coating off I have found that the zinc appears to have penetrated into the base steel and it takes further grinding into the base material to get clean material,this is ok with say 10mm thick plate,but the welding will still spit and bang occasionally,so use bolted construction and only drill holes into the centre line of the channel, do not drill the flanges of the channel,it will serious ly weaken them, If you are converting to a box trailer the way to stiffen the trailer is to make sides from angle iron ,welded at the corners then fill the frame with 12 mm ply and make it a really tight fit so that it becomes a girder section, on light trailers the weakest point is where the trailer "box" meets the drawbar and it may pay to to add some plate to the channel section drawbar , make sure the wheel bearings are well greased and get a spare wheel nearly all trailer problems are old tyres and bearings failing. Also make sure that you inform the car insurance company that you have a tow bar fitted,they are regarded as accessories. some time ago I checked with Direct line about my Discovery ,although it had been fitted from new with a towbar Direct line needed to know,as they regard it as an accessory and must be declared,and updated the policy though there was no extra cost .

I recently replaced the rotting wood base on my farm trailer with salvage steel 'planks'. 2 coats of farm oxide appear to have given it a surprisingly durable finish. Also discovered that the stuff can be sourced in a rainbow selection of colours with minimal prep.

pgk

Doing substantial modification to the trailer i.e. from tent to load carrying would almost certaintly require an new inspection and approval. Many will say "not a problem". Howevert if you get stopped (trailers are often stopped due to level of theft) or have an accident they won't pay your fine or take the point for you... Insurance may be an issue too if you have an accident. If another car is damaged they have to pay the third party, but that does not stop them coming after you to get it back if you had a un inspected trailer.
Up to you to decide on the level of risk you are happy with.

Robert G8RPI.