id quite like to see more indoor sites, like what evike are doing in the US.
Indeed. We aren't in dire need of more scrub woodland sites, we've got those coming out of our ears. Massive open fields? Passchendaele wasn't fun the first time around. Woodland doesn't play to airsoft's strengths, it plays to its weaknesses - unrealistically short range and an inability to punch through foliage.
What we need is more urban/indoor sites. It doesn't have to be bleeding welts CQB, but engagement ranges topping out at 40-50m and averaging 20-30 would be ideal.
if they made the investment you could purpose build something similar to the Erebor black ops setup, which went down incredibly well, however you need the space which there are a fair few in the south and then you need to invest in fitting it out properly.
Nobody's expecting a landlord to spend £500k reconstructing Longmoor; shipping containers aren't that expensive. Container yards are outdoors (obviating the massive expense of renting warehouses for plywood kill houses) and can be put up on the cheapest, crappiest woodland airsoft sites already use. Multistorey is as simple as stacking them on top of each other, you can cut windows and doors in them easily, you can easily bolt internal structures in, and they can be reconfigured and moved easily when the site or the landlord decides it's time for a change. There is a reason that real military training facilities (including in the UK) and a lot of paintball and airsoft sites abroad are built like this.
Most importantly, putting up temporary structures like these don't require "change of use" planning permission. These can go up on land coded for grazing, which is usually a lot cheaper than hardstandings (although those would be much better).
I find it baffling that we have so few of these, and they're so small, when they're downright common in the US. I count only 35 containers in the site below, they haven't even put stairs and railings up to use the roofs and and it's still far bigger than the average airsoft site needs to be.

It's especially useful in the South because they have a far smaller footprint for the same number of distinct spaces than a few barrels and pallets nailed together across a big flat area. Something half the size of a football pitch (when I'd guess the average woodland site is ten or twenty times that) would be perfectly acceptable if it had two storeys of containers on it.
Dirty Dog Airsoft - never been, no idea what it's like - has a pretty minimal yard (looks to be 23 absolutely wrecked containers), and that looks far more interesting than the muddy field it was previously. 10 seconds online - not hunting for the cheapest, most damaged, crappiest containers which would still be more than adequate for sitting in a muddy field on jacks - puts a 40' container at £1,500, which is £3.75/ft2 (half that if you use the roof too) for something you own in perpetuity. For reference, for a warehouse in King's Langley (the same area as Red1's The School) you'll be paying ~£13.00/ft2
per annum for something that you can't take with you when you leave.

I'd really like to see someone take the
£50k it costs to rent a 4,000ft2 warehouse for a year in the South and instead rent a field half the size of a football pitch and put up 30 absolutely rock-bottom containers for a total of 32,800ft2 of one- and two-storey containers with internal rooms, windows, doors, roofs, alleys, courtyards...