I am looking for a HT that matches some specific criteria. Sorry if they appear rather arbitrary. I am looking for a reasonably-priced (so I can afford a few of them) waterproof (I take my radios kayaking).

My use case is that I want an HT that I can use as a mobile rig, take into work for monitoring the repeater, and take kayaking and boating.

I currently have a few FT-270Rs and they fulfill all the requirements, but they are only VHF. There is a quite a bit of activity on 70cm in my AO, and I am missing out with just having a VHF radio.

The VX-7r only has a longer life battery that looks ridiculous, and they are kind of expensive.

Price $ <200 (can be used)
VHF/UHF with relatively easy MARS mod.
OEM 1800mAh li-on battery.
Designated dial for VFO and Volume.
IPX7+ waterproof.

Maybe a Yaesu FT-65R

Thanks for the input, but the FT-65R isn't IPX7 and doesn't have a separate VFO and Volume.

These types of "wish list radio" threads come up occasionally. You will have to compromise and figure out what items on your list are more important.

The Yaesu VX-170 / FT-270 is my favorite go to radio given the IPX-7 standards; its about as milspec as your going to get and is tough as hell.

It's in their capability to make it a dual bander, but they wont.  

The VX-7 I played with wasn't as user friendly as I wanted it to be.

The tri-band VX-8 series has the IPX-7 qualities you seek. I did have, and regret selling off mine.  I didn't have it long enough to get good at using it/menu operation, etc, but regardless, the size/screen was too small for my taste.

Regrettably, I've settled on having a FT-277 on the other hip for when I need to have/monitor two freq's.

An FT270 and FT277 JB Welded back to back will give you the dual band water submersion capability you seek.  

No idea why they don't just make a dual bander that works in that case format.  I get that a lot of their amateur stuff is simply modded from their commercial line, but how hard would it be to implement as a dual bander?  It doesn't necessarily have to be dual receive, just capable of working both bands.