I'm wanting to know how to protect the inside of my build as I am showing the model with the doors open. My build is 1/48 Seasprite 2H-F. I have seen this in photos of the masking but have not found how they do it without attaching it to the outside.

A good question as I will need to do this myself in the near future.
I've seen it done with a cut up piece of sponge, which is probably the easier way but does risk damaging the inside. I would love to know how some modelers mange to get tape neatly inside the door and then remove it.
I have a 1/32 Puma and Lynx in the planning stages that I want to show off with doors open.

I have masked openings by running a thin line of masking tape around the door "jamb" (for want of a better term) perpendicular to the body of the model, and using a toothpick to get it right into the corners. Then I roll up a post-it note into a tube and push it into the opening to prevent any overspray from getting in.

Hope this helps.

Cheers, D

A technique I found that was really good came from a video by a guy who builds commissions that i stumbled over in facebook

Basically soaking wet paper towels. Cheap and efficient
fox three custom models

Used that method of masking myself in the past but had completely forgotten about it, thanks for the reminder.
One thing I do remember about it, is that any weathering pigments /powders you use will have to be sealed. Or the wet tissue will wash them off!