FYI, in a pinch one fall, when my transom mounted skimmer failed, I just propped up a new one inside the bilge in the inch of water that is always there. That got me thru the fall bass run with only an occasional problem when it toppled over.
In the spring I removed the transom mount and sealed over the holes with glass and epoxied the new skimmer to the inside off the hull on the flat area. I guess a picture would help....got it...
I just sanded the area and epoxied using the gel type resin (careful not to make bubbles mixing in hardener).

That one lasted years but the plug corroded so I bought a shoot-thru from LEI.com. That one came with a packet of adhesive. Did need to build a dam with silicone. It has a temp sensor cable to run out to the transom.

They both work great. No problems to 260ft, which is as deep as I've been.

I would never mount a skimmer type outside of the hull ever again.

I thought after my shoot-thru I'd never transom mount another one either, but this one I did...
Were you able to angle yours so it would shoot straight down?...or is it bedded flat to the angle of the hull?...I can't tell from your pics...

angled straight down...they are on the flat parts of the hull (strakes?). The old one is on the port side first strake up from the keel, against the stringer. Here I used gel expoxy keep it angled straight. The new on is the starboard side 2nd strake which is very flat
I wouldn't go out to the farthest one, there will be too much air there.

You could also mount it right in front of the transom drain. On my '84, there is wood glassed into the hull where the bilge pump mounts but there is solid glass for a few inches between that and the transom. Like I said, you can actually just set one there in the inch of bilge water and it works pretty good when its standing upright.

angled straight down...they are on the flat parts of the hull (strakes?). The old one is on the port side first strake up from the keel, against the stringer. Here I used gel expoxy keep it angled straight. The new on is the starboard side 2nd strake which is very flat
I wouldn't go out to the farthest one, there will be too much air there.

You could also mount it right in front of the transom drain. On my '84, there is wood glassed into the hull where the bilge pump mounts but there is solid glass for a few inches between that and the transom. Like I said, you can actually just set one there in the inch of bilge water and it works pretty good when its standing upright.