What should i do before i hang the fenders? Should i paint the inside of the fenders? Coat them with undercoating? They are new aftermarket fenders. Thanks for any and all help.

--Bill

Seal/paint first then use some undercoat,probly rhino bedliner so it won't chip off and start to rust.

I would recommend the following: Scuff, prime and apply body color to inside edges (cut in) just like the factory did. Secure an aerosol rustproof product. 3M has a good one called Rustfighter I. It comes with both a needle and a spray nozzle. Apply to all interior surfaces of fender. Use needle attachment to apply product to interior (boxed) reinforcements and lapped flanges. For the most part these panels lasted for many years without failing, except for boxed in areas. They are the areas that need the most attention. Give it another shot after assembly and painting to all areas where the inner fender attaches, and where it bolts to core support. Even with extreme use this will protect your fenders indefinatly. The Rhino liner is only helpful for areas that are exposed to abrasion, and sound control. Have used this method in Minnesota for collision repair for over twenty years, it works. If you choose, painting the entire inside of fender won't hurt, but may be overkill.
Karl

Unless you plan on driving it in the winter I wouldnt put undercoating or any of the heavy products on them. Most of these cars never see rain again let alone any bad weather. Scuff and shoot some DP 90 on them and you will be fine.