It's possible to do it solo with another controller plugged in. Set the difficulty to the lowest and auto-aim to on.
When you have to do the carrying parts it will get difficult, but you can make it by dropping the item and popping a few guys before moving on. If that gives you trouble, pick up the item and hide behind cover and use the second controller to take out the majority of the enemies before moving on. Always hide the second player somewhere so you can revive yourself and clear more enemies if necessary.
Another tip, always do the furthest possible objective first. For example in the early mission (I forget which one) you have to bomb a bridge in a few different places. After you place a few explosives the enemies will become more plentiful and heavies will appear. If you do the furthest planting locations first (while the enemies are still basic grunts), you have much less distance to travel when the difficulty ramps up.
The moon is glued to a picture of heaven and all the little pigs have God.
I was able to do all the missions except the last one (excluding high tides) and I just asked my friend to come over to help me with the last mission Payback. Then we played PS All Stars so he didn't feel used lmao.