Newpowa 100 Watts 12 Volts Polycrystalline Solar Panel 100W 12V High Efficiency Module RV Marine Boat Off Grid https://www.amazon.com/dp/B00L6LZRXM/ref=cm_sw_r_cp_api_i_XE32BECJ05ZQ37AN4KJ8
Renogy 10A 12V/24V PWM Postive Ground Solar Charge Controller Regulator Compact Design w/LCD Display for Deep Cycle Sealed, Gel, and Flooded Battery, Wanderer PG 10A https://www.amazon.com/dp/B07MVZ777D/ref=cm_sw_r_cp_api_i_S8KRJPTTQE9QKME92Z23
Your friend has shared a link to a Home Depot product they think you would be interested in seeing.
POTEK 500W Power Inverter/Car Inverter DC 12V to AC 110V Dual AC Charging Port and 2A USB Ports for Laptop, Smart Phone https://www.amazon.com/dp/B01MR569GA/ref=cm_sw_r_cp_api_i_TN6EMYQW0M2QVWSHEMZV?_encoding=UTF8&psc=1
I did something similar for my pop up pickup bed camper using stuff similar to these links. Works great. Depending on your needs you could go different size battery or different inverter. Hope this helps…
And i second the comment on propane heater. Tank top one worked fine in my 12x14 shed.
How many watts of panels do you have? If they put out 5-10 amps then you'd spend around the same for a buck converter anw.
I'd recommend you get the Renogy Wanderer 10A, you can program it to different voltage so if you change your mind and decide on 4s instead of 3s you can still use it. It also have the advantages of programmable output setting which you can use to program when your led light power on.
basic PWM charge controller, $17, 7ah 12v battery, $18, 10w solar panel, $26. put it somewhere the panel can get a couple hours of sun a day, the charge controller has USB output to charge your phone.
unless you have other design goals, like trying to make it super portable and want the very minimum panel size, in which case a lot more details of your use and needs would be required.