The 7x6x2 is a nice standard box but only large enough for a RB411 series board. I have a number of these in use in my network with RB411AH boards and the now EOL RB532A boards. I only used the version with the front hinged door held by one screw. They are easier to open and that is important to me for service when hanging on a tower.
http://www.roc-noc.com/product.php?prod ... t=1&page=1
I use the 2nd outdoor box shown with RB433 family and RB600 boards. It is larger than the 7x6x2 and fits the larger RouterBoards. The RB600 still needs the RB604 installed if you want to use more than 2 radio cards in this box.
I have not used the third box shown. If I remember it is made of plastic and not quite as rugged as the die cast boxes.
I don't use fans in my outdoor boxes. With a rotating motor and a rather short life, the fan is a failure waiting to happen and an entry point for insects, water, etc. I don't want that on a tower and it is not needed in most environments.
I have been installing outdoor radios for 10 years and have learned from my mistakes. I don't want something on a tower that requires scheduled maintenance. I try to keep the climbs to a minimum.
Where are you using these and how hot does it get where it needs a fan for cooling?
Tom