i am a regular tourer, (ie my van is not sited) i do not pay for a serivice but i check the gas system with a foot pump if it looses no psi after half hour then the system is good to go, visual checks of the pipe couplings of both water and gas, greese the corner steadies and tow bracket, elec 240v can be checked with one of those plug in system checkers, and the batterie and 12 volt system is simple to check aong the same lines with an electrical tester, the tires are pressure checked and breaks tested while towing, if they work great, i know very quickly if they are binding or not breaking the van at all. most is simple common sence, however for any problems that i come across which are beond my knowlage or indeed unsafe then the mobile caravan man is called for, thankfully i have only had him out once in 2 years for a boiler problem. for damp, dry it, seal it and pray for a good long summer!