ok dudes im the total expert at gummi ships (beat all missions 100% and got the crown gummi *yay!!*)
anyway to answer monkeybutt 1st i suggest u do assault of dreadnaut till u get falcon peak (i use that all the time). now for zaldin, ok the is the best strategy u could want to kill hunter x (i can kill him in 3 hits before he does that 1 hit knockout attack even once=D). ok heres how ya do it. go to gummi creation and make ur own gummi ship. make the entire perimiter of the grid full of normal gummis and make it about 4 gummi blocks wide so that u got a realy big hallow square that u can see straight to the other side, now u have the dumbest ship ever=p now take gummi blocks and add 4 of em to the corner on the front and back so ur ship looks like ur looking at a block with a + shape in the middle. now take some decent lazers and put em on the top 2 corners, and take 2 of the big shields that block enemy lazers and put em at the top and bottom stem of the + shape so it looks like u are looking through a - shape. add 2 cost converters and put a obsorbtion gummi at the top of ur ship and dont even bother adding any wings, cuz u wont need to move much. add lots of those little orange drill gummis on the ship so u can ram stuff with barrel roll and kill almost any ship u touch in 1 hit. now all u gotta do is add auto regins auto life 2 cost converters and a few cannon upgrades. when u do the mission u just sail casually through the mission and when u get to the core just absorb a few shots till ur ship has a big white glow around it and shoot ur weapon and ull kill the core in 1 hit (thats over 100k damage in 1 hit according to the strategy guide!!!) w8 till u get to hunter x and when he does that move where he shoots a boatload of normal pink lazers at u absorb em and shoot (his lazer attack will sail right through the middle of ur ship and u take no damage at all!!!) 3 hits will kill hunter x and thats over 1million damage in 3 hits according to the strategy guide!!!!!!! now u can sit back and laugh that u just whooped the gummi ship boss in 2-3 hits easily (with the auto regins you will beat the mission with almost full hp!)
hope that helps ya and by the way the crown gummi totally sucks cuz it makes u start the mission in berserk mode (yay!!) but 1 hit from any enemy in any mission kills u right away (thats why it sucks) anyway good luck!!!
edit- i just watched the video of u fighting hunter x and i gotta say that its very bad that u didnt have auto regins or auto life upgrades but if u follow this guide you will make it all the way through with almost full hp!!!