Ours is hard to get to as well but I can dump a quart bottle in. Now trans fluid, that's tough, I changed trans fluid a couple months ago. Allison trans, over 3 gallons in gallon jugs. I picked up a small fluid transfer pump at Harbor Freight. They have them at most auto parts stores as well. Another option is a funnel with a long flexible neck. Not sure if that will work for you, you'd have to look at your setup to see.
Hank & Lynda
2003 Winnebago Adventurer 35U