Camel Cut Q's

Thinkin about doing an arch cut on my disco, its a 5 door so is going to be a pain, but have 2 questions before i do it:

1. If i cut the arches away i wil have to remove the plastic wheel arch liner, if this is missing wont all the mud and water get kicked up into the gap between the arch and the inner body?

2. Once you cut the back doors down how do you stick the outer and inner layer together as IRC the outer is ally and the inner is steel?

( i dont think this is a camel cut - as i want to cut the arches all the way round and i dont no what thats called)

iv cut my arches and fitted wide arch plastic offroad ones. and managed to keep most my front liners just needed trimming. with the rears i just hammered the two layers together then the plastic and rubber seals cover the little gap.