Can you tell us more about what kind of vehicles you are building? Are they big enough for people? I'd love to hear more about your experiences around this!
The thing is, most trolling motors for a boat this size run on 12V, because lead-acid batteries are the standard for marine batteries. The energy density of lead-acid batteries is terrible, so you need a pretty big battery for a little tiny boat which doesn't make a lot of sense. You can do a little bit better with a lithium-iron-phosphate battery, but since these are the "new" tech in marine batteries, you pay a really big premium for these which is absurd when you look at the price of the cells themself. So you are paying like 3-5x the price of materials just to get it in a waterproof case.
Also LiFePO4 batteries have a pretty poor energy density when compared to lithion-ion batteries, which are the current standard bearer. The problem with li-ion batteries is that there's not a great way to get them to 12V. Depending on the configuration, you can get a voltage nominal of 10.8V, or 14.4V, both of which put you a little outside the range of what's optimal to power most 12V motors when you're close to min or max voltage. Also there's some advantages to building a 24V battery instead of 12V. Also you have to be really careful about waterproofing, since li-ion batteries are extremely volatile.
So those problems are solvable, and I managed to make a battery which is about the size of a box of tissues, and can power my boat for up to a couple of hours, depending on how many people I bring with me. It's pretty fun to do, and I have all the stuff now, so I'm thinking about doing an e-bike or electric scooter next.
Also I'm thinking about trying to drive the boat with a brushless aquatic thruster, since the trolling motor itself is not that efficient by current standards. But there's a lot of fabrication involved there which I would still have to teach myself.
Regarding the motor, I'd suggest to look at enthusiast RC hardware, which tends to be efficient by necessity: great power density at these sizes is a question of cooling, which is easier if the components are highly-efficient.
And I have been looking at RC motors! The main challenge there would be figuring out how to mount it - those are the skills I think I need to level up a little bit.
It's surprisingly comfortable to carry a lot of weight if you're just heavier than normal.
if it were low power electronics you were powering, I would suggest taking the battery to 14.4v and using some diodes to drop the voltage down a little bit. There would be some power dissipation in the diodes and that would increase with current, so it's probably not a great solution.
It might not be that bad to run the motor out of spec a bit. It sounds like you have a good solution. Did you consider putting the lead acid battery in a towable floatation device of some sort?
In comparison to generic, consumer LiCo, they are better, much better.