POR-15 on undercarriage?

[Vincent72Q]

So it seems I'm in a pickle. I have been using a needle scaler to get the majority of the old factory rubberized undercoating off of my mustang (lots of work but came off pretty easily), there is still a residue in many areas but overall not too much rust underneath it and the coating was still in ok shape around the transmission area from oil/fluid leaks i assume. I still plan on going over the heavier rusted areas with a grinding wheel to clean up any flakey rust. I am wanting to use POR-15 on the entirety of the undercarriage but have some questions I am hoping you may be able to help me with.

A little backstory
The car has no engine or trans its pretty bare. I have removed all brake, fuel lines, and rear suspension so there is absolutely nothing on the undercarriage. I currently have the 9" rear end in the shop being looked at and tuned up so i have no rear axle, the car is in my workshop and I have no way of rolling it out.

Questions:
Por 15 works best on sound rust and bare metal surfaces as long as they are textured a little for the paint to grip. How well do you think it would grip onto old rubberized undercoating residue? Just incase i cant get some areas off.
How should i degrease the undercarriage? Its currently in my shop and I can't move it to hose it down after treating it with purple power.

Thanks for any advice in advance!

-The good son OP