Liners and splash guards...... I use off the rack (actually salvaged from other vehicles) large flat mud flaps, not the supposedly form fit ones, large enough that the trajectory of spray doesn't hit the vehicle. For fender liners, I salvaged them from newer vehicles that came with them; GM started to put them into Tahoe/Suburbans by 2001 or so, and some of those, such as the rears, are close to what we need. My new wife came with a CR-V, that is approaching 300k now, and I'm eyeballing the panels in her wheel wells. I use a heat gun to shape them and stainless fender washers and cap screws to secure, the holes and screws smeared with waxy undercoating. I love my heat gun. I know my local yard well and they let me do what I want out there and I find things I can use. There are currently tons of already shaped plastic liners and underside panels that you can grab and make work. One of the most useful things I have used for flaps is flat rubber material that is sold generically to the trucking industry for them to make their own flaps; large, strong, cuts and drills easy enough to work with. I've lived in the epicenters of rust, New England, Iowa, NYC Metro, and I live within a half mile of the ocean now, and I have survived. I also cheat a little; I get my vehicles from rust free places and start early on rust prevention.
Mad Max, and the others, gave you the secret, the keys to the kingdom; have faith, it can be done.