You can get Solent class plans either from the RNLI Shop (go on the shop home page and go down to the bottom of page) and click on "model making plans" they are 1/12 scale and there are two sheets available at £20 a sheet.
Or there is someone on eBay selling them? Far cheaper as they copies of the original kit plans + templates, not sure of the quality though. Go on eBay search lifeboats in radio control and scroll down?
Graham
