that's good, we're not starting from zero then. take note that some solutions that work for 27mhz band don't work on vhf/uhf, mostly balun and impedance transformer construction. HF baluns use multiple turns of coax or twisted pair through ferrite, on VHF and up it's better to use single turns (ferrite beads) or transmission line baluns (folded balun or sleeve balun). it's also more practical to use some form of transmission line impedance transformers (like quarterwave matching). on vhf and up lumped element tuners are not really a thing, antennas are much smaller so they're just made to match

The particular antenna I was asking about is something I couldn’t DIY

i'm not familiar, if you could describe it in some more detail that can be probably figured out

for 70 cm, i've suggested jpole because it's compact (long and thin), you can probably package it in 30mm or smaller plastic pipe, haul it around, pull out and mount it with a clamp on top of (not parallel to) metal mast and be good to go. you can have metal mast couple cm below shorting bar of jpole, or even a bit away and parallel to for a short run and it shouldn't matter. if needed, radiating part can be mounted parallel to metal mast but needs to be a good distance away (halfwave away or more unless you want to tune it in place). with nonconductive mast the only conductor nearby is coax. it would be 50cm-ish long so good for mobile setup. these are fast and cheap, the way i've made them the most expensive part was plastic box, can be made and tuned with nanovna in a single evening

groundplane antennas would be even shorter but much bulkier, unless you detach radials or mount them on a kind of swivel mount, and you have to put them in the air, as in, bottom end of radials can't be too close to ground. mast considerations are pretty much as jpole, as in, the hub can be mounted on top of metal mast but not parallel and right next to it. if folded, 2m version would be about 50cm long, so it'll probably make sense on 2m and down. you can probably make a 70cm band quarterwave whip attached to magnet so that you can put it on roof of your car, but it won't be as good because height is might here, and jpole has center of radiation half wave above mounting point just because of the way it's built. just that little bit of extra height might clear some obstructions. straight dipoles should also work, but they're T-shaped unless disassembled, and you'll have to run coax perpendicular to dipole for some length to avoid common mode current problems -> not as simple mechanically, fine for horizontal not so much for vertical

you could also make a small (5-7 el? depends on how long do you want it) 70cm band yagi and store it on top of your radio box, but you'll need to put it on a mast then rotate it, or hold it in your hand, preferably standing on a hill or something when in use. stiff jpole would be probably fine for 70cm, 2m if you can accommodate the length, lower than that, 2m to probably down to 6m or 10m, rollup jpoles should work okay as long as you have a way to deploy them. below that it's probably mast + some kind of halfwave dipole territory (efhw? doublet? series of center fed dipoles? ocfd? some type of vertical? you decide)