Having all our stuff at the range allows us to load up what we want to test, retest, and avoid loading up a bunch of stuff that doesn't work or that we have to take apart.
Many of the shooters at Deep Creek 1000 yd BR range bring a travel trailer with their loading stuff and test all day. It allows for very extensive testing.
The problem with just seating bullets long is that you don't have the ability to fine tune your powder charge. At Deep Creek, we think in most cases powder charge testing allows us to stay better in tune. Once found, seating seems to stay in tune well by chasing the lands, but sometimes we don't need to chase the lands the full amount. Ideally, we should test both powder and seating to be optimally tuned for the match the next day.
A way to do both powder and seating testing without bringing a trailer or a portable power supply is to preload small glass vials with powder. Let's say I want to test four powder charges and four seating depths. I would need to prep and prime 24 cases and 60 powder charges. 12 powder charges in loaded ammo and 48 powder charges in glass vials. I would shoot the powder ladder, then load up the best powder charge to check seating depth.
When the load is refined and only needs minor tweaking before a match, it could be done with seating first. Again, we need 24 cases prepped and primed, but we'd only need 24 powder charges. 12 in the loaded ammo then another 12 to check powder charges after finding seating. The big issue with this is you need to be pretty close with your initial powder charge.
Or we could go all out and do powder, seating, and powder again.
With whatever else we want to test, like neck tension, primers, primer crush, etc., we can figure out how many glass vials to load with powder and then seat at the range with a portable press--the arbor press probably being the simplest.