That sounds like a good plan, in principle, but sub MR86 instead of MR84, for currency. Either way, you will need antennas with them. How would you uplink them to the network? Wired connection is definitely preferable.
You could mesh them though, if cabling is not possible and if an existing gateway (wired) MR is near enough. Your choice of antennas may well have an effect on that - MR84/6 is dual-band, with the 4 antenna posts serving both 2.4 GHz and 5 GHz, so you can't have one antenna optimised for mesh uplink and one serving the clients. (You could do that with MR74/6 where each radio has its own pair of antenna posts, but those AP models arent so powerful, for the qty of users here)
I would look at the ANT-20 first (qty 2 = 4 antennas) and check you'll get good mesh uplink, without the need for directional antennas. If you have to go directional, your coverage within the tent will likely suffer - unless your directional antenna is placed to have both the clients and the gateway AP in the direction of signal travel.
The APs would be mounted with the antennas pointing straight up and straight down - probably pole mounted, out of reach of people in the tent itself.
