Vonoventwin, you have asked an excellent question. First of all I would agree that putting yourself upside down on your home is scary, and not something I normally recommend. However you closed on your home already upside down by $8,000. So we can approach this simply form a savings standpoint, and I hope that you are in some sort of fixed interest mortgage program on your 1st mortgage.
I put together an amortization schedule based on the loan terms you listed $48K loan @13.5% with you paying $1,800 a month. It is the link below:
http://www.mortgage-calc.com/mortgage/loan.php I am a mortgage broker and have been one for about 6 years with 5 more years in finance. I am by no means an expert, but if you really tie yourself to $1,800 a month payment you will be paid off in 2.7 Years. Also the interest you pay is tax deductible on the mortgage depending on your tax situation consult your CPA to verify. If you take 2.7 years x 12 months= 32.4 months x $1800= $58,320 - 48,000= $10,320 extra it will cost you to pay off your debts going this route.
The second mortgage/ lien will have to be paid off with your new mortgage. Will the $8,000 kill your deal?
I lend in Tennessee hence my screen name, but we are only allowed to go to 115% LTV here. I have never sold this loan option to a customer or even presented it as an option. I do not know your entire situation, but it does seem like an option that may actually provide some benefit for you.
So now the thing to do is determine how long $1,800 a month against all of your current debt minus the tax deduction will take to pay off. How much extra is that goign to cost you?
Here are some great calculators to help you figure this out:
http://www.mortgage-calc.com/index.html http://www.drcalculator.com/