Yes you can. Unless you have a completely inexperienced filler, it will be recognized as a horizontal tank and filled on a scale until the bleeder bleeds liquid just as if it were vertical, or to it's measured weight as most tanks are filled.
Mike
2012 Winnebago Impulse Silver 26QP
2005 16.6 Double Eagle
2018 Jeep Wrangler JK
previously Snowbird Campers,
Triple E Motorhome and Fifth Wheel