Questions about tubs

[chosen2030]

I'm running out of space and considering buying/buiding a rack system. I do have questions about the tubs though. I have browsed and viewed many rack systems and most seem to have 3 things in common - arrangement, no lids and open front. So my questions are:

1) Why do most rack systems have the tubs slide in from the short end instead of from the length of the tub (e.g. that's where the handles ususally are, keeps the bins darker for the snakes/disrupts them less, temps/heating, looks better, easier to find a space for it in your house, etc)?
2) Why don't you want to use lids on your tubs? If the space above the tub is tight, obviously pulling the entire tub out to open it to feed and clean would be a pain, but if you leave room above the tub, could you use one with a lid or are the husbandry issues (e.g. temps, humidity, disease, stress to animal, etc) that make it preferable not to use lids?
3) Why do racks have an open front? My wife would prefer not to be able to see the pastic tubs and asked if something could be used to cover the front. What are the issues with covering the front (e.g. heat, ventilation, etc) or what would be safe ways to cover/obscure the front?

Thanks!