[UPDATE] - I loaded the map in Lagoon TP(only) and resaved it so there should be no conflict with multi env. TP's now.
This is a sample map of a new "Tube" item set I am working on.
The Tube item set is finished now and on Maniapark:
Lagoon-Tubes
It took a while to finish the set because I wanted to add Start, Finish, Checkpoint and Multilap Gates to it which we can now make in the item editor.
TIP: if you have trouble taking corners in the tubes try to either drive straight through them or try turning slightly the opposite way you think you should.
IE: At first checkpoint, try driving straight forward through the twists.