Extend-a-Stay question

vacation or extended stay ?

I would Not do it

if both are full, you are going to run low on both
if one is half and one is full, the higher pressure full one is going to bleed over to the other one until they are equal
then consume both at the same time, yes it will last longer

you run the risk of running out and having nothing at all

if the portable runs out you can turn it off and open the frame tank

keep to {2} portable cylinders,
connect one, when its low, change it
less likely to run out that way

I agree there is no issue with opening both tank valves and they will both draw down while in use but at some point they will both be empty. At the same time.

Don't see a problem but the big question,except which tank will be consumed first? Main, portable or will both run out at the same time?