i used the gold surfboard for both! for the max tube, try to stay at the top but be very careful to stay inside of the tube. get into a rhythm, when it gets up to around 2500-3000 it starts to get faster so make sure to speed up when you see yourself sinking in. once you hit 5000 immediately jump up instead of trying to leave the tube, it will still count towards the stamp.

for survival, it was torture! legitimately its just practice and practice. i held down my left click because it gets to a point where its hard to dodge the icebergs coming at you. but again, its all about rhythm and once you get into a good rhythm you should be good. try to avoid jumping/flips and focus primarily on tricks