I am pretty sure that VOSA and the police in general for that matter wouldnt bother going outside the mart on monday mornings - would be too much paperwork for them
- they could make a tidy trade stood next to the washbay giving out tickets for broken lights, wrong number plates, 'un-taxed' 0 tax rated tractors, homemade trailers, trailers with no internal lights, trailers with odd tyres, trailers without breakaway cables blah blah blah lol
As long as you dont drive like a fool pretty much any trailer will do in my opinion, yes you can make it more comfortable with bedding and wadding if you like. Just take it steady and think ahead.
You may want to check what kind of unloading area they have at the mart though - they should have access for lorries as thats what they normally leave in but it may be worth seeing if they can take the size of lorry you intend to unload from.
I use a horse trailer to transport mine around - they dont like it down the mart as its got no side gates but its the only trailer I've got.
Baz