hi robert i use an ecotemp L10 from corwoods(it comes with gas regulator).a 13kg gas bottle and car radiator hose from hot outlet to reel.
IMO the L10 is much better(and bigger!)than an L5 and ive had no problems with pressure building up and blowing connectors/hoses etc.
i leave one back door open when in use(its fitted just inside the back of the van).
just make sure you have a good sturdy all metal reel and good tight connectors and hoses that can handle the hot water.
when changing gas bottles always spray new connections with a soapy solution then turn the gas on.if you see any bubbles appear DO NOT USE!refit the connector until no bubbles are present and then your good to go.