How about one of these?
https://www.amazon.com/Wise-Adjustable-Boat-Pedestal-Black/dp/B000KKET70/ref=sr_1_12?dchild=1&keywords=RV+Pedestal+Captains+Chair&qid=1572286982&sr=8-12
or
https://www.recpro.com/pedestal-for-rv-captains-chair/