My dog same problem
My dog just had the same problem about a month ago, he had 3 very large tumors removed from his under arm, ribs, and chest. After the first 10 days he had to be brought to his vet again and she moulded a body cast over him, he was ripping his drainage tubes out and holes were present, we did not add stitches. After a week or so, cast came off and it healed up nicely, then about a week later stitches (the ones that were left!) were removed. It does take quite some time for these major operations to heal. My dog wore a t-shirt for weeks to keep him from scratching an licking. You really do have to limit their activity, and it was very hard knowing he was in pain and I could not do anything about it. He is now starting to go for walks and on the way to recovery.
"You should treat your dogs so good; you wish you were them!" -Adogsday