Has anyone moved their fuse fuse panel from under the dash to a more easily accessed / serviced location? I'm thinking the engine compartment would be a better location. (This is for a driven car, so originality is not important.)

Some newer vehicles have a fuse panel in the engine compartment. The ones I've seen were large, ugly plastic boxes. Are there any decent salvage yard options? Are there any QUALITY aftermarket fuse panel that can be mounted in an exterior location?

What kind of vehicle?? It can be moved anywhere you want but doing so, and doing it correctly for longevity / reliability is not going to be and easy task. Think close to a complete rewire.
Due to the cost and labor involved one may ask how often do you need to change a /fuse?? Not trying to be a smarta-- just helpful

The wiring harness needs to be replaced. The original harness has been cut and hacked by the previous owner(s). It also appears to have some rodent damage! It is a mess!! I also want to add some extra equipment and circuits. (A/C, sound system, trailer towing harness, etc.)

If the electrical system was good, I'd leave the fuse panel where the factory mounted it!

I did a 12V-Neg Ground-Alternator conversion a couple years ago on a guy's '53 Ford PU.
Used American Autowire due to past good experience with them.
Mounted fuse box at the interior firewall, left of steering column, for easy access.
Not a fan of fuse box locations where they can get wet or hot or oily.

With that info, I'll agree with Topside and suggest American Autowire. Depending on the vehicle they may offer one of their "update series" or you can go with A hiway 15 or 22 series. the 15- 22 series is a 'custom kit" that allows you to do whatever you want.
Again depending on the vehicle, If you are using the stock switches etc. that may require you to source the terminals/ connectors. Call them and they can probably supply them as well.
We use AA almost exclusively on our non stock applications.

I thought about moving my fuse panel until I realized I only replace fuses once or twice every couple of years. A lot of work with very little return.

I will in the future repair or replace the fuse box with one that has better contacts. The fuses and contacts get corroded over time and that leads to fuse/wire heat up and failures.

I am working on an under hood panel for one of my cars with all the extras in it but leaving the factory fuses and circuits alone. It will have stuff like headlight and fuel pump relays, vacuum pump relays and fuses, etc. I have looked on Amazon and plan on using one like this but with better contacts.

I am not endorsing this particular one but I am going with this style.

https://www.amazon.com/ONLINE-LED-S...K1/ref=pd_bxgy_img_2/139-8196044-0252245

That would be good to mount up front for headlight, fan and horn relays.

You'll notice that on newer vehicles they have TWO fuse boxes - one inside the passenger compartment under the dash and one in the engine compartment which also houses relays.

The bulk of the inside fuses are for interior options - radio, cig lighter, dome lights, etc.. This minimizes the amount of wire needed as opposed to running wires from an external panel.

On my son's 89 ramcharger, when we ditched the TBI and went 4 barrel AFB, we wanted to eliminate the fusible links, while at the same time make those circuits remain fused and able to change said fuse instead of cutting out fusible links because fusible link wire is not easily solder-able, neither of us like butt connectors or scotchloks, especially under the hood. So along with retrofitting an 87 harness to the truck, we went scouting the junkyard and found a small under hood fuse box from I forget what, think it was a late 90s zx2 and incorporated that info the factory harness. We were looking for a small fuse box with the"big" fuses. There are enough spots in the fuse box for all of the circuits that we're previously fusible linked plus a few extra spots for future add one like off-road lights, stereo equipment, CB, etc.

Using the Eaton Series 1530x-x style fuse/relay box. It uses Metri-Pack 280 terminal connectors, and can come in different configurations.
The specific one I have is the series 15305-2.
Got it pre-wired with the relays and fuses from Amazon:
https://www.amazon.com/gp/product/B01FWILL20/ref=ppx_yo_dt_b_asin_title_o06_s00?ie=UTF8&psc=1

But I should have just ordered the box non-wired as I will just use the Metri-pack 280 terminals crimped on the wiring so I don't have to make wire splices.
That box series # has the fuses bussed to the main power, and one side of the relays activation coil bussed. I needed 2 relays activated on the high side for the headlights, and the other 3 activated on the low side for cooling fans, horn (or A/C compressor)
so I cut the relay side buss, and soldered a ground wire to the upper/end part of the bus. The first 3 relays are still on the stock buss connection that is connected to power through one of the fuses.

The 1530x-4 series is the un-bussed box if you need to mix switched and unswitched power, but it will be a few exrea wires ti make the connections to create the power busses.