Plastic shorts

Hello, I have very bad psoriasis but the worst area with complete coverage is my buttocks, thighs and calves. I find it hard to apply Dovobet or Enstilar everywhere now that my beloved husband has died and I cannot hang around naked easily because I have MS and need to sit down. I put in cotton pj bottoms once greased up but feel that a lot of the ointments are soaked up by them. I have tried sticking sheets of cling film to the ointment for a while but it's nigh on impossible for me to do to myself. What I need is effectively so plastic shorts or trousers I cannot put on for a while, and which can be machine washed. I'm also plus size. Can anyone recommend anything? I'm suddenly wondering about rainproof trousers if it's possible to get them in a 26. Hmm. Thank you for reading this!