Exactly SI... on my old boat,(which was a sixties or seventies fairline)... we took the cooker out and used portable gas, it saved on getting pipework and regultors replaced. Tidy wiring,marking up of fuel tanks etc etc,
A word of warning, ask your tester what fire extinguisher he wants to see BEFORE you go buy one, not all "halfords" type ones are acceptable!
I think generally the testers are ok, most are boat owning plumbers (you had to be corgi regd originally i think to do the testing)... Most will point you in the right direction of what needs to be done to get the cert....
On another note... if the boats have been used in the sea, remember that the salt corrodes ally fairly well, The hull wont suffer, (unless it's VERY OLD!)... but the engine and any chandelry could need a bit of care. This may be relevant to something like a leeky output shaft seal, that looks like a simple job, but results in the problem being a corroded casing rather than a shagged seal?..
Boats are fantastic fun, and a great aid to fishing, i regret selling mine, but you really have to get the use out of it to warrant keeping it, esspecially in a marina round these parts, as munkey will know!