Then I took a 425 gallon tank which is mounted on a utility tariler and I filled it half full of wtare and towed it to a place that is approximately 5 feet higher than the ballcock valve in the toilet * * *
It might be worth considering:
You have 100 feet of garden hose between the tank and the PVC plumbing in the Spartan trailer. Gravity feed is marginal to get the water from the tank to the trailer, so you're considering a pump.
If you have an outside sillcock back at the house, with "typical house" water pressure, and if the Spartan trailer is within about 250 feet of the house, it might be simpler just to run up to 250 feet of garden hose from the pressurized house plumbing.
Extensive/repeated experience (largely at WVA) indicates that "normal" 35 - 40 psi at the sillcock will push 1.5 gpm or more through 250 feet of 3/4" garden hose. This would probably be sufficient to provide "minimum sanitary accomodations" for your guests.
The flow is a little less with the (usually) cheaper 5/8" hose, but might be good enough, although the cheapest stuff doesn't tend to stand sustained pressure as well and might swell up after a while, especially in hot weather. Good quality 5/8" hose is out there, but you may have to check the details to get one that is rated for "sustained pressure."
I've only had to run more than 250 feet of hose at WVA (during lineups) twice, and got "usable(?)" flow even at about 325 feet; but the flow, even for a wide open outlet, drops off pretty quickly beyond the 200 or 250 foot distance.
"usable(?)" means I could fill the coffee pot in about the time it took to drink the last (16 oz) cup from the previous pot (60 oz). It doesn't include brewing the next pot before the cup goes dry. (It's a campground definition.)