Chasing rust!

So the 06 MK2 elegance sailed though it's MOT this week with only a single advisory for a rusty rear subframe. I have treated with lanoguard which appears to have halted further rust around the frame/arms etc so will keep up a once yearly treatment. Also managed to inject lots of lanoguard into both sills through the rubber bungs which will hopefully stop it rusting from the inside out. 

The external sills have a couple of light rust patches but still v solid and also a tiny bit appearing around the wheel arch lips. 

I'd like to remove the plastic undertrays and arch liners to treat these areas too.  Has anyone done this? Worried what I might find and also whether it'll be a massive ball ache to get them on/off. Will mean a jack/axle stands too. Expect I'll need new screws all round as doubt they'll be in a fit state to re-use. If anyone knows the size/type I would need to order that would be much appreciated!