my 1st caravan just been serviced and has damp!!

I bought my 1st caravan a few weeks ago and was over the moon :) I wanted the gas,electric etc checked before using her so booked her in for a service. She is a 1991 Bailey Pageant De Ville.She was serviced on Friday and was finished today...they picked up a few faults that amount to £366 inc service charge of £150 but to my horror they showed me on diagrams of the caravan how much damp there is in her :'(.... the readings vary from 25%-70% mainly at the front and the back..the people who we bought her off said there had been a leak but it had been repaired...what they meant was they stopped the leak but didn't treat the damage :(...the caravan shop said it would cost £2-3 000 to sort her out...my Hubby is a competant DIYer would he be able to do the repair as really we don't want to give up on her...the service man said the inside fixtures were in fantastic condition so we really would love to give her a chance on taking us on holiday :) any comments will be greatly appreciated :) thank you