Coupla thoughts.
Cable weight vs. altitude.
I've got 60' of RG8x that came with my Shakespeare 5215 Whip

It's very light and has low loss. I haven't weighed it, but the whole length can't be more than a couple of pounds. I'm not worried about the weight. If it's that easy to blow this boat down, I'm on the wrong boat.
VHF is line of sight and for most a deck mounted antenna is fine. Most powerboats live with this configuration without complaints. However, altitude does increase range.
For me, we boat on a large lake (30 miles long) with few other boaters. The main emergency monitoring station is on the other end of the lake. My handheld VHF at "sea" level can't reach that end even at 10 miles. Plus we have lots of hills that can get in the way.
As much as the hassle of drilling is going to be, I'm opting for the top of the mast.
Terry wrote:I just used Gorrilla glue where the tubes join, one goes partway inside the other. Downside is once you get the first 10' section thru you glue the second 10' section to the end then wait a couple hours for it to dry before continuing the cutting job. So go have lunch!

Interesting. I assumed you used a standard PVC coupler like this

The obvious problem is that the coupler increases the diameter of your
drill bit. But I know that properly glued, the coupler won't come apart. The Gorilla glue idea sounds nice, but my fear is that if it breaks apart mid drilling, I'm stuck with 10' of PVC in there that I can't get out.
Also, you said, "one goes partway inside the other". How do you get 2 PVC pipes to join like this? Do you taper the outside of one and the inside of the other?
I'm thinking of your glue idea and perhaps put a wire or something inside the first pipe as a safety. If the PVC coupling breaks, I could pull the first PVC pipe back out. Another idea is to take a coupler like above and attach it to the leading PVC pipe and carve teeth into it. This would be my drill bit and would bore a hole wide enough to accommodate my coupler later down the pipe.
I'm planning on doing this mod this weekend. How hard is that foam? Is it easy to cut into or hard like a Styrofoam cooler.
eg: Running the cable down the deck.
If you don't mind seeing it, that is the ideal. No connectors means no loss.
I'm too anal to stand to see cable running down the deck and I'm gonna have to figure out a deck connector. I had one on my last boat and had excellent performance. Some kind of rubber boot to keep water out should do the trick.
Thanks for posting your drill bit idea. I would have given up once opening that bugger up and seeing foam.