Put more into the vehicle thus burdened (7)
I believe the answer is:
saddled
'thus burdened' is the definition.
'saddled' can be an answer for 'burdened' (I've seen this before). I am not sure about the 'thus' bit.
'put more into the vehicle' is the wordplay.
'put more' becomes 'add' (I can't explain this - if you can you should believe this answer much more).
'into' indicates putting letters inside.
'the vehicle' becomes 'sled' (sled is a kind of vehicle).
'add' placed into 'sled' is 'SADDLED'.
Can you help me to learn more?
(Other definitions for saddled that I've seen before include "Having to put up (with) - ready to be ridden" , "Horse might be" , "Ready to ride" , "Burdened with" , "Like a racehorse" .)