Spot on. The more you can process your foods the easier it will be, and make sure to drink calories. Add a container of Fairlife milk daily, or cheap regular milk if you tolerate lactose well. Sodas, juice, intra carbs can add cals quick. High cal protein powders.
Ground meat, adding healthy oils, condiments like guacamole and mayo, mashing your potatoes, white/rice pasta, white rice, keep the fiber to things that don’t fill you like oranges, ground flax, etc. Adding something sweet after every meal like a piece of fruit or granola bar is another 500 cals per day of quick carbs.
It will always be tough. You will not be hungry and you are going to have to force it often. I have gained 26lbs in 6 weeks. Almost every night I have to make a mental decision to fight through my last meal. But I am big and strong as ever.