Servicing a caravan is not that difficult if you are technically minded. However, as a mobile engineer myself I would discorage any work on any appliance that has a gas supply and similarly any appliance running from 240volt. The essence of any service is knowing what to look for and knowing when things aren't working correctly, For example, I check the DC and/or current being pulled by the various electrical appliances when operating, this way I know whether the heating elements are working correctly. Also you should do gas leak tests annually and check the date on the gas hoses. Again its not sufficient to be able to check these things, it is essential that the results when checking are interpreted correctly. In any event work on gas systems should only ever be undertaken by an approved gas engineer. In respect of the brakes and running gear, again it is important to understand how the whole brake system operates. Its not just a case of adjusting the shoes at the hubs as an incorrect setting here may prevent the auto reverse mechanism operating or the hand brake working correctly. If you are happy to do certain checks yourself, then I am sure a mobile engineer would be happy to just do the gas side, or chassis work. Hope this helps. Paul