thanks so much for your help guys, I've been sifting through and trying to get my head around it all.
NB the boat will still be in the boat shed in which it is being finished, so not on the water, and sheltered in some way though only in a big shed)
I'm unable to fully go with the Tankguard for cost reasons, so have searched and got to the following.
Plan 1 is as follows, for next Saturday (set temp to be 14 high, 8 low in the night prob)
firstly, get a little heater and have it in the box where/when poss
1 sand it a little by hand
2 hoover that out
3 paint one coat of Sikagard 62 (5kg should cover around 20m2, the tank is about 14m2)
4 Go home and have a bath / work for a week while the boat gets finished and moved to the yard (would work on it crack any curing paint etc?)
5 Come back and paint a second coat around 7-10 days later *
* https://www.promain.co.uk/amfilerating/file/download/file_id/8051/ this says i need to wait BETWEEN 30 hours and 3 DAYS which worries me as next week i can't do that timing.
I know this is not perfect but it's built off of what i can afford money / timewise as i work 6 days a week at the moment and its 50 quid each way to get to the boat itself..
PLAN 2 is to wait a few weeks and do it when i can actually be there for longer (a saturday - a monday) when it might be warmer (who knows though), and me and a few v generous friends are going up to do the exterior painting. The process would be the same, but instead of 7-10 days later I can do it in the advised time bracket on the application guidelines
My boatbuilders just advised me to come and paint it asap, basically, so they can close it up for me, hence the feeling that i should rush.
Thank you again