My guess is that putting the entire printer in a plastic bag or sealed tub won't be effective, even if it is truly hermetically sealed. There would be enough air in there for the ink to dry out.
Evaporation takes place from both ends of the "ink system". Each cartridge has an air hole to let air in as ink leaves the cartridge (otherwise, you couldn't get the ink out of the cartridge). The cartridge, itself, is sealed before you install it. You could put a piece of tape over the air hole in each cartridge to reseal that end.
The other end is the nozzles of the printhead. When the head is parked, it is sealed against a tank of absorbent material. This is where the ink goes when the printer runs the nozzle cleaning cycle. That seal is better than nothing, but it isn't completely effective; the printhead will still dry out over time.
Even the factory sealed cartridges have a limited shelf life (often on the order of a year). So if you can reseal things, it will help, but 2 1/2 months is a long time.
If the printhead is a user replaceable part, it is usually pretty straightforward to remove it. In that case, you could remove and reseal the ink tanks, and remove the printhead and clean it to remove all of the ink. However, in some printer models, the ink tanks don't go directly in the printhead. They go into a fixed area on the printer and there is internal plumbing to get the ink to the printhead. In that case, there won't be an effective way to seal things, and you risk ruining the printer if you leave the ink tanks out.
The HP manual indicates that you should not remove ink cartridges once they are installed. As ridiculously expensive as the ink is, the bigger issue with long-term non-use is the printhead. They can get clogged to an extent that they require heavy-duty cleaning outside of the printer or replacement. That's one drawback of inkjets--you have to keep using them.
I would look for a way to have the printer print something maybe once a week. If there is no simple way to set that up, lend it to a friend and ask them to occasional print something or do a nozzle test or print-head alignment just to move some ink through the printhead.