I rent so I didn't want to drill any holes, obviously.
But a window A/C unit I put into the window near where my station was left about a 1" gap on each side. I moved the AC to one side to get a 2" gap, and on the inside I use the plastic thing it came with to "block" the hole on the inside. On the outside I cut a piece of 3/4" plywood to fit the gap, leaving a 2" gap at the bottom.
When I have to run coax through, I just remove the screw on the inside, stick the coax under and out through the hole.
The gap is filled with foam insulation, and I pack the area the coax goes through with a sandwich bag filled with small packing peanuts, I kind of wrap it around the cable bundle.
Grounding is accomplished outside since a water spigot is right there, although I'm also working on getting a ground rod in as well. The patio is poured concrete, but its well over 20 years old so the wood they used to create "gaps" in it about 1" wide is rotting away. I plan on putting a rod about 5" away from the house so its not easily tripped over in one of those gaps.
The electric panel is grounded to the same spigot so everything will tie together.
I would get more elaborate but since I don't know how long I will be in this rental I'm doing my best to do things that will not leave too many holes, etc. I do like a lot of the ideas here for sure, and will think of them if I ever do purchase a home, but for now I have to work with what I have. I'll feel a lot better about things when I have a good ground rod at the entry way, even though California overall doesn't get nearly the amounts of lightning (at least where I am) compared to other places.
When I leave the rental the only evidence of Ham Radio should be the ground rod and a few holes where I attached push up poles for verticals.
Ironically when I was looking for a spot for the pole I put my vhf/uhf vertical on, I found a ground rod against the garage right where I was planning on putting it. It is there because the garage is detached and has a sub-panel with 4 breakers in it for the garage lights, etc. I will keep it in mind as well if I add or modify antennas in the future.
And I like your setup for sure, N6AM. I worked you on 20 if you were the /5 operating within the past few weeks. Your antenna system likely pulled my little 25W into an inverted V right out no problem