The body was discovered on 15 August 2017, but officers are still trying to find his next of kin to let them know.
A driving licence, birth certificate and a newspaper from August 2016 were also found in the tent.
However, Avon and Somerset Police say they have not been able to confirm his identity “due to the condition of the remains”.
The man was found off the A370 near Weston-super-Mare.
Investigating officer PC Andy Henderson said: “This is a really sad case of a man who appears to have been sleeping rough and whose death seems to have gone unreported.
“It would appear he had been dead for up to a year before he was found and due to the condition of the remains it has been extremely difficult to establish for certain who he is.
“Based on the documentation found, we believe the man to be called Peter Thomas Harrison who was born in Birmingham and would either have been aged 59 or 60 when he died.
“We also believe he was a driver by trade and had spent recent years in and around the Weston-super-Mare area.
“We’d rather his next of kin not find out about his death in this manner but feel strongly that given the length of time, it is important they know.”
:: Anyone with information is asked to call 101 with the reference 5217187006.