inflator OR compressor?
tank or tankless?
hard wired or not?
12v or 120v ?
pressure rating and duty cycle?
and the most important question, how much $$ do ya wanna spend?
-first lets solve the 35 ft of 12v cord issue...
there are 12 outlets INSIDE the stream, so use them when inflating the trailer tires...
using the trailer outlets means a 10-20 ft COILED 12v extension cord solves the distance issue...
(be aware of the amp/volt requirements and limitations of these extension cords)
skip looking for a battery version it will be expensive and have VERY limited utility.
-at 100$ or less there are a couple of directions 4 a portable 12v or a small 120v...
the small tankless 12v inflators WILL air up a tire, but take a lOOOOOng time doin it.
for example going from 55psi to 65 psi might take 10-15 minutes PER tire.
i carried and used one of these for 5 years and it worked ok.
slow, but it would eventually get the tires UP to pressure, and it still works fine.
many versions but this one is adequate at 50$ and i still use it occasionally.
search the brand/name online, i had LOW expectations for this 35$ purchase but it worked fine, still does.
because i wanted something with more UMMMMPH! a small 120v was purchased.
see post #5 here...
with the small (1 gallon?) tank, it was much faster to inflate and can be used to blow out the lines too...
lots of versions and brands in the 100$ price range, but one does need AC juice (or a genset) to use it...
again still in service at 5 years but as the garage compressor now.
last year i added a 12v HARDWIRED compressor and reservoir tank to the truck...
it's installed UNDER the bed (inside the double wall) on the frame rail
a couple of companies market these but they are available from 100s of truck accessory websites and stores...
VIAIR Corporation - Portable Compressors
these are 200-500$ with pumps rated for 25% up to 100% duty cycles...
the duty cycle is HOW LONG the pump can run continuously...
relative to how HOW LONG it must be rested 2 avoid OVER heating and failure.
this is important when inflating large tires like those on the truck or trailer.
with/out a tank they also make portable versions of the airlift/viair noted above,
that either plug into a 12v round outlet or connect to the battery POSTS...
typically they come in a bag with a long coiled air hose like this...
again many versions and price points and vendors (camping world, and most truck enthusiast stores)
there are versions at harbor freight for less money but durability may be an issue.
mine is 100% duty cycle, does tires quickly and will blow out lines and even work with LOW volume air tools.
the tank is always FULL of compressed air at 170 psi, for a speedy tire or blowing job...
it's probably more than most folks want or need.
many other examples in these threads and the LINKS within...
so again sort of price point and features when choosing, from the many options.