I think I've found the right carrier!
It meets BA requirements in that it's
1. Big enough for all each of my cats to be more than comfy in.
2. Vents on all four sides, secure enough (door zip ties closed), strong enough? I assume
3. Door can not be opened by accident (if zip tied)
4. No nose or paw can fit through mesh (no more than any other carrier)
5. .....So how IS the water and food accessible from the outside anyhoo?
This is the exact kennel I used for 5 of my cats. I sourced mine from a local pet supply store in Dallas, TX. If you haven't ordered it yet, contact your local shops to see if they have them. Since I was buying multiple kennels, I was able to work out a discount for a bulk purchase.
The size was perfect for them. Each kennel had a water absorbent pad (part of travel kit) at the bottom, on top of that was a cat blanket (purchased from Walgreens) and on top of that was a cat bed (purchased from Walgreens).
For water, I purchased a hamster bottle. The dish that was provided with the travel kit was placed under the bottle to catch any leakage. Bottle similar to this but sourced locally for less...
Travel kit: I sourced this locally for $2.99...
For food, I provided BA a ziploc bag of their food which was then kept by London Heathrow animal receiving as it contained meat products.
I did not need to ziptie the door as it was very secure and was tough to open normally.
Everything went really smooth from the BA side as well as Heathrow receiving. I even let the flight attendants know that I was the crazy lady with the 5 cats below and they were gracious enough to keep me informed of their status on board.
Don't hesitate to pick my brain some more.