Check the rating plates on each unit for watts or amps used. I'd add 30 to 40 percent to that so you are not running near the max. Example, if the tv is 200 watts and the dvd is 50 watts, i'd go with a 350 to 400 watt inverter.
If the tv is installed and you can't get to the rating plate easilly, check the manual or maker's website. You can also measure the actual draw with a meter if you have one.
If you buy a modified sine wave unit, make sure that you can return it if it doesn't work well with your electronics. Some stuff requires pure sine wave power to work well.
2008 Itasca Meridian 37H & 2015 Flagstaff T12RBST
2011 & 2012 Len & Pat's "One lap of America"
27K miles & 41 states in 13 months - Woo Woo
Yellowstone Lake 6-1-2012