It looks like you have a true vintage item there -- nearly 45 years old! I don't know if you'll find another Landau owner here, as there are mainly fiberglass travel trailer owners on this forum. But I'm sure you can get (and find) lots of advice on how to clean your fiberglass exterior, along with advice about appliances, sealing windows
, plumbing, electrics... the whole shebang.
How many miles does your Landau have?