What size is your board and how big are you? The funboard you're riding probably has a good deal of volume, floats like a champ, and paddles like a dream. The give take to that ease of paddle and float comes at the sacrifice of ease of duckdiving and other manhandling aspects of surfer and board/shape. Pushing all that buoyant foam down and under a peeling/breaking wave can be difficult, especially a few waves in a row.

Are you able to duckdive it well on occasion, or does it get increasingly more difficult as you're duckdiving multiple waves in a row from a set as fatigue sets in or as technique begins to fall at the wayside?

When I was first learning, I would swim my big ass fun shaped board out instead of paddling it out. Throwing it over the top of cresting waves as they approached if they were gentle enough or holding on tight to the leash nearer to the leash plug where the velcro is if it was a more powerful wave.

Boards like that are easier to paddle out at reef/point breaks where you can utilize a channel, but if you're surfing beach breaks it can be difficult to paddle out a board with a lot of volume that's hard to duckdive. Apart from the techniques already mentioned, the timing of your paddle can be key. Due to the ease of paddling, if you can time it so your energy is focused on paddling during a lull in the sets, you can conserve a bit of energy compared to trying to power through the waves unable to duckdive them.