Is moving to Samsung an option? The latest Tab Active rugged models have dual band GPS in them getting submeter right out of the box. Plus can use in the rain, hot swap batteries, etc.
We are hoping the dual band from the iPhone makes it to the iPad soon but I have not seen anything on it yet.
In our testing we found that a bad elf was no better than the iPad esp in canopy. You really need something with a big antenna to make a difference in canopy like an Arrow from Eos.